Bus termination

Discussion in 'The Projects Forum' started by Regected, Oct 23, 2010.

  1. Regected

    Thread Starter Active Member

    May 24, 2009
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    This is my first project designing a PCB, and it is a doosy. The project is a BASIC stamp microcontroller to drive 72 sets of LEDs. I'm using 8 outputs from the stamp as inputs to 9 latches. 4 more outputs from the stamp are run to a 4 to 16 demultiplexer, which is used to select an individual latch to set it's output. Do I need to terminate the 8 output bus to ground through resistors? The bus runs for approximately 4 inches with a 5v signal and less than a 20mA load. It will be operating no higher than 20kHz, so my gut says no, but i figured I would ask anyway.

    Attached is the sch file from ExpressSCH just in case I lot you with my description.
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    I cannot open the .sch file using eagle .
    Am I missing something?
     
  3. SgtWookie

    Expert

    Jul 17, 2007
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  4. John P

    AAC Fanatic!

    Oct 14, 2008
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    To answer the question--it's a short line, and slow signals. So this is one place where you can skip the terminations.
     
  5. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Express....Did not use it before.
    And it's free too. Coooooool.
     
  6. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    As others said short distance does not need termination.
    What kinda environment are planning to have it in?
     
  7. Regected

    Thread Starter Active Member

    May 24, 2009
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    This is going to be used like a consumer level product, so no extreme temperatures nor moisture. It's actually going into a beer pong table. Just have to make sure spills on the table won't get the electronics.
     
  8. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    I meant noise. RF interference
     
  9. marshallf3

    Well-Known Member

    Jul 26, 2010
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    Small spills can become large ones in drinking games, I'd pot it in clear polyurethane or acrylic resin. The stuff is cheap enough and available from most large hobby shops, they use it to make those decorative paperweights out of.
     
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